This invention relates to polysilanes which are useful as preceramic polymers in the preparation of ceramic materials and articles. This invention further relates to the methods of preparing such polysilanes as well as the ceramics prepared from such preceramic polymers.
Baney et al. in U.S. Pat. No. 4.310,651 (issued Jan. 12, 1982) disclosed a polysilane of general formula (CH.sub.3 Si)((CH.sub.3).sub.2 Si) where there was present 0 to 60 mole percent ((CH.sub.3).sub.2 Si) units and 40 to 100 mole percent (CH.sub.3 Si) units and where the remaining bonds on silicon were attached to other silicon atoms and chlorine atoms or bromine atoms. The polysilane was converted to a beta-silicon carbide containing ceramic material at elevated temperatures (about 1400.degree. C.). The polysilanes of U.S. Pat. No. 4,310,651 generally are difficult to handle due to their high reactivity in air.
Baney et al. in U.S. Pat. No. 4,298,559 (issued Nov. 3, 1981) prepared polysilanes of general formula (CH.sub.3 Si)((CH.sub.3).sub.2 Si) where there was present 0 to 60 mole percent ((CH.sub.3).sub.2 Si) units and 40 to 100 mole percent (CH.sub.3 Si) units and where the remaining bonds on silicon were attached to other silicon atoms and additional alkyl radicals of 1 to 4 carbon atoms or phenyl radicals. Upon heating these polysilanes were converted into silicon carbide containing ceramics in high yields.
Baney et al. in U.S. Reissue Patent Re. 31,447 (reissued Nov. 22, 1983) disclosed polysilanes of the general formula (CH.sub.3 Si)((CH.sub.3).sub.2 Si) where there was present 0 to 60 mole percent ((CH.sub.3).sub.2 Si) units and 40 to 100 mole percent (CH.sub.3 Si) units and where the remaining bonds on silicon were attached to other silicon atoms and alkoxy radicals containing 1 to 4 carbon atoms or phenoxy radicals. Silicon carbide-containing ceramics were obtained by firing these polysilanes to elevated temperatures.
Baney et al. in U.S. Pat. No. 4,314,956 (issued Feb, 9, 1982) disclosed polysilanes of the general formula (CH.sub.3 Si)((CH.sub.3).sub.2 Si) where there was present 0 to 60 mole percent ((CH.sub.3).sub.2 Si) units and 40 to 100 mole percent (CH.sub.3 Si) units and where the remaining bonds on silicon were attached to silicon and amine radicals of the general formula --NHR''' where R''' is a hydrogen atom, an alkyl radical of 1 to 4 carbon atoms or a phenyl radical. A silicon carbide-containing ceramic was obtained by firing this polysilane to an elevated temperature under an inert atmosphere or under an ammonia atmosphere.
The just discussed U.S. Pat. Nos. 4,310,651, 4,298,599, Re 31,447, and 4,314 956 are hereby incorporated by reference. These polysilanes are further discussed in Baney et al. Organometallics, 2, 859 (1983).
Haluska in U.S. Pat. No. 4,546,163 (issued Oct. 8, 1985) which is hereby incorporated by reference prepared polysilanes of the average formula (RSi)(R.sub.2 Si)(R''.sub.d (CH.sub.2 .dbd.CH)Si) where there was present from 0 to 60 mole percent (R.sub.2 Si) units, 30 to 99.5 mole percent (RSi) units, 0.5 to 15 mole percent (R''.sub.d (CH.sub.2 .dbd.CH)Si) units, where the remaining bonds on silicon are attached to other silicon atoms and chlorine atoms or bromine atoms, where R is an alkyl radical containing from 1 to 4 carbon atoms, where R'' is an alkyl radical containing 1 to 4 carbon atoms, a vinyl radical, or a phenyl radical, and where d is 1 or 2. Polysilanes of the same average formula but containing additional alkyl, aryl, alkoxy, aryloxy, substituted amine, or unsubstituted amine radicals attached to silicon were also prepared. These polysilanes could be pyrolyzed at elevated temperatures in an inert atmosphere to produce silicon carbide-containing ceramics. The vinyl-containing polysilanes could be cured, and thus rendered infusible, prior to pyrolysis by exposure to ultraviolet light.
West in U.S. Pat. No. 4,260,780 (issued April 7, 1981) prepared a polysilane of general formula ((CH.sub.3).sub.2 Si)(CH.sub.3 (C.sub.6 H.sub.5)Si) by the sodium metal reduction of dimethyldichlorosilane and methylphenylsilane. The resulting methylphenylpolysilanes had very high softening points (greater than 280.degree. C.).
West et al. in Polym. Prepr., 25, 4 (1984) disclosed the preparation of a polysilane of general formula (CH.sub.3 (CH.sub.2 .dbd.CHCH.sub.2)Si)(CH.sub.3 (C.sub.6 H.sub.5)Si) by the sodium metal reduction of allylmethyldichlorosilane and methylphenyldichlorosilane. These polysilanes were rapidly gelled by irradiation with ultraviolet light.
What has been newly discovered are polysilanes of the general formula (R.sub.2 Si)(RSi)(R'Si) where there are also bonded to the silicon atoms other silicon atoms and chlorine or bromine atoms, where R is an alkyl radical containing 1 to 4 carbon atoms, and where R+ is selected from the group consisting of alkyl radicals of at least six carbon atoms, phenyl radicals and radicals of the formula A.sub.y X.sub.(3-y) Si(CH.sub.2).sub.z wherein each A is independently selected from a hydrogen atom or alkyl radicals containing 1 to 4 carbon atoms, y is an integer equal to 0 to 3, X is chlorine or bromine and z is an integer greater than or equal to 1. These polysilane preceramic polymers can be pyrolyzed at elevated temperatures under an inert atmosphere to yield ceramic materials or articles. These polysilanes may also be converted into other preceramic polymers which can be pyrolyzed to ceramic materials or articles. These polysilanes represent a significant advance in the art of preparing ceramic materials or articles, especially in the art of preparing ceramic fibers.